Amorphization under fracture surface in hydrogen-charged and low- temperature tensile-tested austenitic stainless steel

ABSTRACT

The microstructure just below the fracture surface in hydrogen-charged stable austenitic SUS 316L stainless steel, which was subjected to a low strain rate tensile test at ?70°C, was studied by a combination of the focused-ion-beam method and transmission electron microscopy. An amorphous region with a chemical composition almost identical to that of the polycrystalline region was found under the lath-like structure on the fracture surface, although no deterioration of tensile properties by hydrogen appeared. In the amorphous region, band-like regions with wavy contrasts were observed, which were often accompanied by cracks at the boundaries. The presence of the amorphous region with band-like regions implies that amorphization occurred due to high-density vacancies accompanied by agglomerations of excess vacancies in the hydrogen-charged SUS 316L stainless steel that was tensile-tested at low temperatures.     

骨延长的骨愈合原理

骨延长愈合与骨折愈合等多种多样的骨修复现象可能具有相同的细胞生物学基础,这个理论称为骨修复一元论.血管内皮细胞是启动骨修复的感受器,破骨细胞通过分泌骨形态发生蛋白（BMP）启动骨特异性修复.骨折间隙间断性的力学脉冲通过血管内皮细胞不断地转化为骨修复的生物学脉冲.在微损伤条件下,骨修复具有放大效应.保护下负重和功能锻炼是下肢骨骼延长术后的重要原则.     

Effect of strain rate on the compressive behaviour of a Zr56Al10.9Ni4.6Cu27.8Nb0.7 bulk metallic glass

We report the study of the effect of strain rate on the compressive behaviour of a Zr₅₆Al_10.9Ni_4.6Cu_27.8Nb_0.7 bulk metallic glass. The results indicated that both the strength and plasticity of the glass increase with increasing the strain rate up to 10^?5 s^?1, above which the strength and plasticity start to decrease. The enhanced mechanical properties under a strain rate of 10^?5 s^?1 are due to the emission/propagation rate of the shear bands being consistent with the strain rate.     

Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy: an in situ study

ABSTRACT

The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy.     

The kinetics of infralow-frequency viscoelastic internal friction induced by irreversible structural relaxation of a metallic glass

This letter presents the results of internal-friction measurements of Co 70 Fe 5 Si 15 B10 metallic glass at temperatures 400K h T h 700K and frequencies 0.01 Hz h f h 0.05Hz. It is shown that Maxwellian viscoelastic damping is predominant in this case. The nature of this damping is determined by irreversible structural relaxation. The kinetic relaxation law is derived.     

A theory of work softening

Observed features of the yield drop in work softening support the view that the structure in a slip band is heterogeneous in a metal such as aluminium or copper. The centre of the band is almost empty of dislocations. These are concentrated round its boundary, particularly as walls of edge dipoles at its ends. It is argued that work hardening is due to the prevention of the passage of these dislocations by a forest of obstacles with small activation volumes and energies. Thermal energy enables them to cut through their obstacles and so to penetrate further into their walls, thereby reducing their back stress and enabling the Frank-Read sources, within the bands, to become active at lower applied stresses. The yield drop is explained as due to an overshooting, resulting from this thermally activated cutting, of the stress to operate the sources.     

A statistical model of cleavage fracture in structural steels with power-law distribution of microcrack size

Based on the well-accepted physical understanding that cleavage fracture of structural steels is preceded by plastic deformation, a critical flaw in the Beremin model and its modifications is proposed, and a new statistical model with the power-law distribution of microcracks is obtained to describe the cumulative probability of cleavage fracture. A set of cleavage fracture toughness data of a nuclear pressure vessel steel is used to highlight the difference between the new model and the Beremin model.     

Strong interactions between hydrogen in solid solution and stress-induced martensite transformation of Ni–Ti superelastic alloy

The role of the dynamic interactions between hydrogen in a solid solution and the stress-induced martensite transformation in hydrogen embrittlement has been investigated using trained Ni–Ti superelastic alloy. In a cyclic tensile test in the stress plateau region caused by stress-induced martensite and reverse transformations after hydrogen charging, a further decrease in the critical stress for the martensite transformation is observed. In addition, the number of cycles to fracture for a trained specimen is significantly larger than that for a non-trained specimen. Since most of the charged hydrogen is preferentially trapped in defects induced by training, the hydrogen embrittlement is considerably suppressed as a result of decreasing interactions between the hydrogen and the transformation. The present results indicate that hydrogen in a solid solution more strongly interacts with the stress-induced martensite transformation than hydrogen trapped in defects, thereby further enhancing the hydrogen embrittlement related to phase transformations.     

骨折治疗方法与原则的最优化历程

多年来骨折治疗,新旧技术、新旧理论相互融合,相互碰撞,产生了新的理论和方法,使得临床疗效显著提高,现阶段理智的临床医生应该融汇各家之长,多方互补,对每一位骨折患者的治疗都应该按照最优化的原则进行.但是在医疗过程中总存在着如方法选择不当或者错误,过度治疗,医患信任危机,医疗伦理道德的丧失等情况,我们应该用矛盾分析的方法来思考这些问题.     

老年髋部骨折围手术期医疗风险的分析与对策

髋部骨折是老年人的常见病之一,髋部骨折对老年人生命的危害最大。随着人口老龄化,老年髋部骨折发病率呈逐年上升趋势。老年骨质疏松髋部骨折围手术期的医疗风险临床较常见,如何降低老年骨质疏松髋部骨折围手术期的医疗风险,是临床骨科需要解决的问题。分析存在的风险问题,明确各种风险因素,尽可能降低老年髋部围手术期的医疗风险。